1. Field of the Invention
The present invention relates to a thermal developing apparatus for thermally developing a latent image, which is formed on an image forming layer of a thermally developing recording material, by heating the thermally developing recording material.
2. Description of the Related Art
In recent years, the thermal developing apparatus and the thermal developing/recording apparatus that never applies the wet process and uses the dry system have been proposed. In such thermal developing apparatus and such thermal developing/recording apparatus, the photosensitive and/or thermal recording material (photosensitive/thermal recording material) or the film-like recording material containing the thermally developing photosensitive material (referred to as a “thermally developing recording material” hereinafter) is used as the recording medium. Also, in the thermal developing apparatus and the thermal developing/recording apparatus using the dry system, the latent image is formed by radiating (scanning) the laser beam onto the thermally developing recording material in the exposing portion, then the thermal development is carried out by bringing the thermally developing recording material into contact with the heating means in the thermal developing portion, and then the thermally developing recording material on which the image is formed is discharged to the outside of the apparatus.
There is the thermal developing apparatus having the heat plate, which is arranged to come into surface-contact with the thermally developing recording material to be carried, as the heating means provided to the thermal developing portion. In case the thermally developing recording material is heated by using the heat plate, a temperature difference is generated in respective regions where the thermally developing recording material comes into contact with the heat plate, and then unevenness of a density is sometimes generated in the thermal developing/recording apparatus after the development. For this reason, a plurality of heating portions each having a heating surface of the heat plate, which is obtained by dividing the contact surface of the thermally developing recording material into plural regions, are provided and then these plural heating portions are controlled by controlling devices at the time of thermal development respectively, so that it is prevented that such unevenness of the density is generated in the thermally developing recording material after the development (see JP-A-2004-101679, for example).
FIG. 5A is a view explaining a configuration of the thermal developing portion of the thermal developing apparatus in the related art, and FIG. 5B is a graph showing a heating temperature at respective positions of the heat plate of the thermal developing portion in FIG. 5A.
As shown in FIG. 5A, in the thermal developing apparatus to which a heat plate 1 consisting of a plurality of heating portions 2, 3, 4 was provided, a plurality of temperature measuring portions 5a, 5b, 5c such as a thermistor, or the like were provided to the thermal developing apparatus to control appropriately a temperature of heating surfaces of respective heating portions 2, 3, 4. Then, the temperature was measured at center positions of the heating surfaces of the heating portions 2, 3, 4 respectively in the direction that is perpendicular to the carrying direction of the thermally developing recording material F (the lateral direction in FIGS. 5A and 5B).
Meanwhile, the temperature was low at the end portion of the heat plate 1 in the direction that is perpendicular to the carrying direction of the thermally developing recording material F, and the temperature was high near the center region. Thus, as shown in FIG. 5B, the temperature was changed in the direction that is perpendicular to the carrying direction of the thermally developing recording material F. Therefore, a difference was caused between the temperature measured by the temperature measuring portions 5a, 5b, 5c and the ambient temperature of measuring portions of the heat plate 1. Thus, it was extremely difficult to control the heating portions 2, 3, 4 respectively such that the heat plate 1 should be kept at a substantially constant temperature as a whole at the time of thermal development.
Also, as shown in FIG. 5A, in the case where the temperature was measured at the center positions of the heating portions 2, 3, 4 by the temperature measuring portions 5a, 5b, 5c respectively, when the temperature at the regions near the end portions of the heat plate 1 (portions indicated by P1 and P4 in FIG. 5B) is kept at a predetermined temperature T (about 120° C.), the so-called overheating was generated in the center portions the temperature of which was higher than the regions near the end portions (portions indicated by P2 and P3). As a result, in some cases the unevenness of the heating temperature was generated in the heat plate 1.